Extreme ultraviolet mask absorber materials

ABSTRACT

Extreme ultraviolet (EUV) mask blanks, methods for their manufacture and production systems therefor are disclosed. The EUV mask blanks comprise a substrate, a multilayer stack of reflective layers on the substrate, a capping layer on the multilayer stack of reflecting layers, and an absorber on the capping layer. The absorber comprising a plurality of bilayers comprising a first layer of silicon and a second layer selected from the group consisting of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, Pt, oxides of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, Pt, and nitrides of TaSb, CSb, TaNi, TaCu, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, and Pt.

TECHNICAL FIELD

The present disclosure relates generally to extreme ultravioletlithography, and more particularly extreme ultraviolet mask blanks andphase shift masks with an absorber comprising a first layer and a secondlayer and methods of manufacture.

BACKGROUND

Extreme ultraviolet (EUV) lithography, also known as soft x-rayprojection lithography, can be used for the manufacture of 0.0135 micronand smaller minimum feature size semiconductor devices. However, extremeultraviolet light, which is generally in the 5 to 100 nanometerwavelength range, is strongly absorbed in virtually all materials. Forthat reason, extreme ultraviolet systems work by reflection rather thanby transmission of light. Through the use of a series of mirrors, orlens elements, and a reflective element, or a mask blank, coated with anon-reflective absorber mask pattern, the patterned actinic light isreflected onto a resist-coated semiconductor substrate.

The lens elements and mask blanks of extreme ultraviolet lithographysystems are coated with reflective multilayer coatings of materials suchas molybdenum and silicon. Reflection values of approximately 65% perlens element, or mask blank, have been obtained by using substrates thatare coated with multilayer coatings that strongly reflect light withinan extremely narrow ultraviolet bandpass, for example, 12.5 to 14.5nanometer bandpass for 13.5 nanometer ultraviolet light.

FIG. 1 shows a conventional EUV reflective mask 10, which is formed froman EUV mask blank, which includes a reflective multilayer stack 12 on asubstrate 14, which reflects EUV radiation at unmasked portions by Bragginterference. Masked (non-reflective) areas 16 of the conventional EUVreflective mask 10 are formed by etching buffer layer 18 and absorbinglayer 20. The absorbing layer typically has a thickness in a range offrom 51 nm to 77 nm. A capping layer 22 is formed over the reflectivemultilayer stack 12 and protects the reflective multilayer stack 12during the etching process. As will be discussed further below, EUV maskblanks are made on a low thermal expansion material substrate coatedwith multilayers, a capping layer and an absorbing layer, which is thenetched to provide the masked (non-reflective) areas 16 and reflectiveareas 24.

The International Technology Roadmap for Semiconductors (ITRS) specifiesa node's overlay requirement as some percentage of a technology'sminimum half-pitch feature size. Due to the impact on image placementand overlay errors inherent in all reflective lithography systems, EUVreflective masks will need to adhere to more precise flatnessspecifications for future production. Additionally, EUV blanks have avery low tolerance to defects on the working area of the blank.Furthermore, while the absorbing layer's role is to absorb light, thereis also a phase shift effect due to the difference between the absorberlayer's index of refraction and vacuum's index of refraction (n=1), andthis phase shift that accounts for the 3D mask effects. There is a needto provide EUV mask blanks having an absorber which mitigates 3D maskeffects.

SUMMARY

One or more embodiments of the disclosure are directed to an EUV maskblank comprising a substrate; a multilayer stack which reflects EUVradiation, the multilayer stack comprising a plurality of reflectivelayer pairs; a capping layer on the multilayer stack which reflects UVradiation; and an absorber on the capping layer, the absorber comprisinga plurality of bilayers comprising a first layer of silicon and a secondlayer selected from the group consisting of TaSb, CSb, TaNi, TaCu, SbN,CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, and Pt, oxides of TaSb, CSb, TaNi,TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, and Pt, and nitrides ofTaSb, CSb, TaNi, TaCu, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, and Pt.

Additional embodiments of the disclosure are directed to method ofmanufacturing an extreme ultraviolet (EUV) mask blank comprising formingon a substrate a multilayer stack which reflects EUV radiation, themultilayer stack comprising a plurality of reflective layer pairs;forming a capping layer on the multilayer stack; and forming an absorberon the capping layer, the absorber a plurality of bilayers comprising afirst layer of silicon and a second layer selected from the groupconsisting of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd,Co, Ag, Pt, oxides of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re,Os, Cd, Co, Ag, Pt, and nitrides of TaSb, CSb, TaNi, TaCu, Cr, Ir, Pd,Re, Os, Cd, Co, Ag, and Pt.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

FIG. 1 schematically illustrates a background art EUV reflective maskemploying a conventional absorber;

FIG. 2 schematically illustrates an embodiment of an extreme ultravioletlithography system;

FIG. 3 illustrates an embodiment of an extreme ultraviolet reflectiveelement production system;

FIG. 4 illustrates an embodiment of an extreme ultraviolet reflectiveelement such as an EUV mask blank;

FIG. 5 illustrates an embodiment of an extreme ultraviolet reflectiveelement such as an EUV mask blank; and

FIG. 6 illustrates an embodiment of a multi-cathode physical depositionchamber.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the disclosure, it isto be understood that the disclosure is not limited to the details ofconstruction or process steps set forth in the following description.The disclosure is capable of other embodiments and of being practiced orbeing carried out in various ways.

The term “horizontal” as used herein is defined as a plane parallel tothe plane or surface of a mask blank, regardless of its orientation. Theterm “vertical” refers to a direction perpendicular to the horizontal asjust defined. Terms, such as “above”, “below”, “bottom”, “top”, “side”(as in “sidewall”), “higher”, “lower”, “upper”, “over”, and “under”, aredefined with respect to the horizontal plane, as shown in the figures.

The term “on” indicates that there is direct contact between elements.The term “directly on” indicates that there is direct contact betweenelements with no intervening elements.

Those skilled in the art will understand that the use of ordinals suchas “first” and “second” to describe process regions do not imply aspecific location within the processing chamber, or order of exposurewithin the processing chamber.

As used in this specification and the appended claims, the term“substrate” refers to a surface, or portion of a surface, upon which aprocess acts. It will also be understood by those skilled in the artthat reference to a substrate can refer to only a portion of thesubstrate, unless the context clearly indicates otherwise. Additionally,reference to depositing on a substrate can mean both a bare substrateand a substrate with one or more films or features deposited or formedthereon.

Referring now to FIG. 2, an exemplary embodiment of an extremeultraviolet lithography system 100 is shown. The extreme ultravioletlithography system 100 includes an extreme ultraviolet light source 102for producing extreme ultraviolet light 112, a set of reflectiveelements, and a target wafer 110. The reflective elements include acondenser 104, an EUV reflective mask 106, an optical reduction assembly108, a mask blank, a mirror, or a combination thereof.

The extreme ultraviolet light source 102 generates the extremeultraviolet light 112. The extreme ultraviolet light 112 iselectromagnetic radiation having a wavelength in a range of from 5 to 50nanometers (nm). For example, the extreme ultraviolet light source 102includes a laser, a laser produced plasma, a discharge produced plasma,a free-electron laser, synchrotron radiation, or a combination thereof.

The extreme ultraviolet light source 102 generates the extremeultraviolet light 112 having a variety of characteristics. The extremeultraviolet light source 102 produces broadband extreme ultravioletradiation over a range of wavelengths. For example, the extremeultraviolet light source 102 generates the extreme ultraviolet light 112having wavelengths ranging from 5 to 50 nm.

In one or more embodiments, the extreme ultraviolet light source 102produces the extreme ultraviolet light 112 having a narrow bandwidth.For example, the extreme ultraviolet light source 102 generates theextreme ultraviolet light 112 at 13.5 nm. The center of the wavelengthpeak is 13.5 nm.

The condenser 104 is an optical unit for reflecting and focusing theextreme ultraviolet light 112. The condenser 104 reflects andconcentrates the extreme ultraviolet light 112 from the extremeultraviolet light source 102 to illuminate the EUV reflective mask 106.

Although the condenser 104 is shown as a single element, it isunderstood that the condenser 104 can include one or more reflectiveelements such as concave mirrors, convex mirrors, flat mirrors, or acombination thereof, for reflecting and concentrating the extremeultraviolet light 112. For example, the condenser 104 can be a singleconcave mirror or an optical assembly having convex, concave, and flatoptical elements.

The EUV reflective mask 106 is an extreme ultraviolet reflective elementhaving a mask pattern 114. The EUV reflective mask 106 creates alithographic pattern to form a circuitry layout to be formed on thetarget wafer 110. The EUV reflective mask 106 reflects the extremeultraviolet light 112. The mask pattern 114 defines a portion of acircuitry layout.

The optical reduction assembly 108 is an optical unit for reducing theimage of the mask pattern 114. The reflection of the extreme ultravioletlight 112 from the EUV reflective mask 106 is reduced by the opticalreduction assembly 108 and reflected on to the target wafer 110. Theoptical reduction assembly 108 can include mirrors and other opticalelements to reduce the size of the image of the mask pattern 114. Forexample, the optical reduction assembly 108 can include concave mirrorsfor reflecting and focusing the extreme ultraviolet light 112.

The optical reduction assembly 108 reduces the size of the image of themask pattern 114 on the target wafer 110. For example, the mask pattern114 can be imaged at a 4:1 ratio by the optical reduction assembly 108on the target wafer 110 to form the circuitry represented by the maskpattern 114 on the target wafer 110. The extreme ultraviolet light 112can scan the EUV reflective mask 106 synchronously with the target wafer110 to form the mask pattern 114 on the target wafer 110.

Referring now to FIG. 3, an embodiment of an extreme ultravioletreflective element production system 200 is shown. The extremeultraviolet reflective element includes a EUV mask blank 204, an extremeultraviolet mirror 205, or other reflective element such as an EUVreflective mask 106.

The extreme ultraviolet reflective element production system 200 canproduce mask blanks, mirrors, or other elements that reflect the extremeultraviolet light 112 of FIG. 2. The extreme ultraviolet reflectiveelement production system 200 fabricates the reflective elements byapplying thin coatings to source substrates 203.

The EUV mask blank 204 is a multilayered structure for forming the EUVreflective mask 106 of FIG. 2. The EUV mask blank 204 can be formedusing semiconductor fabrication techniques. The EUV reflective mask 106can have the mask pattern 114 of FIG. 2 formed on the EUV mask blank 204by etching and other processes.

The extreme ultraviolet mirror 205 is a multilayered structurereflective in a range of extreme ultraviolet light. The extremeultraviolet mirror 205 can be formed using semiconductor fabricationtechniques. The EUV mask blank 204 and the extreme ultraviolet mirror205 can be similar structures with respect to the layers formed on eachelement, however, the extreme ultraviolet mirror 205 does not have themask pattern 114.

The reflective elements are efficient reflectors of the extremeultraviolet light 112. In an embodiment, the EUV mask blank 204 and theextreme ultraviolet mirror 205 has an extreme ultraviolet reflectivityof greater than 60%. The reflective elements are efficient if theyreflect more than 60% of the extreme ultraviolet light 112.

The extreme ultraviolet reflective element production system 200includes a wafer loading and carrier handling system 202 into which thesource substrates 203 are loaded and from which the reflective elementsare unloaded. An atmospheric handling system 206 provides access to awafer handling vacuum chamber 208. The wafer loading and carrierhandling system 202 can include substrate transport boxes, loadlocks,and other components to transfer a substrate from atmosphere to vacuuminside the system. Because the EUV mask blank 204 is used to formdevices at a very small scale, the source substrates 203 and the EUVmask blank 204 are processed in a vacuum system to prevent contaminationand other defects.

The wafer handling vacuum chamber 208 can contain two vacuum chambers, afirst vacuum chamber 210 and a second vacuum chamber 212. The firstvacuum chamber 210 includes a first wafer handling system 214 and thesecond vacuum chamber 212 includes a second wafer handling system 216.Although the wafer handling vacuum chamber 208 is described with twovacuum chambers, it is understood that the system can have any number ofvacuum chambers.

The wafer handling vacuum chamber 208 can have a plurality of portsaround its periphery for attachment of various other systems. The firstvacuum chamber 210 has a degas system 218, a first physical vapordeposition system 220, a second physical vapor deposition system 222,and a pre-clean system 224. The degas system 218 is for thermallydesorbing moisture from the substrates. The pre-clean system 224 is forcleaning the surfaces of the wafers, mask blanks, mirrors, or otheroptical components.

The physical vapor deposition systems, such as the first physical vapordeposition system 220 and the second physical vapor deposition system222, can be used to form thin films of conductive materials on thesource substrates 203. For example, the physical vapor depositionsystems can include vacuum deposition system such as magnetronsputtering systems, ion sputtering systems, pulsed laser deposition,cathode arc deposition, or a combination thereof. The physical vapordeposition systems, such as the magnetron sputtering system, form thinlayers on the source substrates 203 including the layers of silicon,metals, alloys, compounds, or a combination thereof.

The physical vapor deposition system forms reflective layers, cappinglayers, and absorber layers. For example, the physical vapor depositionsystems can form layers of silicon, molybdenum, titanium oxide, titaniumdioxide, ruthenium oxide, niobium oxide, ruthenium tungsten, rutheniummolybdenum, ruthenium niobium, chromium, antimony, nitrides, compounds,or a combination thereof. Although some compounds are described as anoxide, it is understood that the compounds can include oxides, dioxides,atomic mixtures having oxygen atoms, or a combination thereof.

The second vacuum chamber 212 has a first multi-cathode source 226, achemical vapor deposition system 228, a cure chamber 230, and anultra-smooth deposition chamber 232 connected to it. For example, thechemical vapor deposition system 228 can include a flowable chemicalvapor deposition system (FCVD), a plasma assisted chemical vapordeposition system (CVD), an aerosol assisted CVD, a hot filament CVDsystem, or a similar system. In another example, the chemical vapordeposition system 228, the cure chamber 230, and the ultra-smoothdeposition chamber 232 can be in a separate system from the extremeultraviolet reflective element production system 200.

The chemical vapor deposition system 228 can form thin films of materialon the source substrates 203. For example, the chemical vapor depositionsystem 228 can be used to form layers of materials on the sourcesubstrates 203 including mono-crystalline layers, polycrystallinelayers, amorphous layers, epitaxial layers, or a combination thereof.The chemical vapor deposition system 228 can form layers of silicon,silicon oxides, silicon oxycarbide, tantalum, tungsten, silicon carbide,silicon nitride, titanium nitride, metals, alloys, and other materialssuitable for chemical vapor deposition. For example, the chemical vapordeposition system can form planarization layers.

The first wafer handling system 214 is capable of moving the sourcesubstrates 203 between the atmospheric handling system 206 and thevarious systems around the periphery of the first vacuum chamber 210 ina continuous vacuum. The second wafer handling system 216 is capable ofmoving the source substrates 203 around the second vacuum chamber 212while maintaining the source substrates 203 in a continuous vacuum. Theextreme ultraviolet reflective element production system 200 cantransfer the source substrates 203 and the EUV mask blank 204 betweenthe first wafer handling system 214 and the second wafer handling system216 in a continuous vacuum.

Referring now to FIG. 4, an embodiment of an extreme ultravioletreflective element 302 is shown. In one or more embodiments, the extremeultraviolet reflective element 302 is the EUV mask blank 204 of FIG. 3or the extreme ultraviolet mirror 205 of FIG. 3 or an EUV phase shiftmask. The EUV mask blank 204 and the extreme ultraviolet mirror 205 arestructures for reflecting the extreme ultraviolet light 112 of FIG. 2.The EUV mask blank 204 can be used to form the EUV reflective mask 106shown in FIG. 2.

The extreme ultraviolet reflective element 302 includes a substrate 304,a multilayer stack 306 of reflective layers, and a capping layer 308. Inone or more embodiments, the extreme ultraviolet mirror 205 is used toform reflecting structures for use in the condenser 104 of FIG. 2 or theoptical reduction assembly 108 of FIG. 2.

The extreme ultraviolet reflective element 302, which can be a EUV maskblank 204 or EUV phase shift mask, includes the substrate 304, themultilayer stack 306 of reflective layers, the capping layer 308, and anabsorber 310. The extreme ultraviolet reflective element 302 can be aEUV mask blank 204, which is used to form the EUV reflective mask 106 ofFIG. 2 by patterning the absorber 310 with the layout of the circuitryrequired.

In the following sections, the term for the EUV mask blank 204 is usedinterchangeably with the term of the extreme ultraviolet mirror 205 forsimplicity. In one or more embodiments, the EUV mask blank 204 includesthe components of the extreme ultraviolet mirror 205 with the absorber310 added in addition to form the mask pattern 114 of FIG. 2.

The EUV mask blank 204 is an optically flat structure used for formingthe EUV reflective mask 106 having the mask pattern 114. In one or moreembodiments, the reflective surface of the EUV mask blank 204 forms aflat focal plane for reflecting the incident light, such as the extremeultraviolet light 112 of FIG. 2.

The substrate 304 is an element for providing structural support to theextreme ultraviolet reflective element 302. In one or more embodiments,the substrate 304 is made from a material having a low coefficient ofthermal expansion (CTE) to provide stability during temperature changes.In one or more embodiments, the substrate 304 has properties such asstability against mechanical cycling, thermal cycling, crystalformation, or a combination thereof. The substrate 304 according to oneor more embodiments is formed from a material such as silicon, glass,oxides, ceramics, glass ceramics, or a combination thereof.

The multilayer stack 306 is a structure that is reflective to theextreme ultraviolet light 112. The multilayer stack 306 includesalternating reflective layers of a first reflective layer 312 and asecond reflective layer 314.

The first reflective layer 312 and the second reflective layer 314 forma reflective pair 316 of FIG. 4. In a non-limiting embodiment, themultilayer stack 306 includes a range of 20-60 of the reflective pairs316 for a total of up to 120 reflective layers.

The first reflective layer 312 and the second reflective layer 314 canbe formed from a variety of materials. In an embodiment, the firstreflective layer 312 and the second reflective layer 314 are formed fromsilicon and molybdenum, respectively. Although the layers are shown assilicon and molybdenum, it is understood that the alternating layers canbe formed from other materials or have other internal structures.

The first reflective layer 312 and the second reflective layer 314 canhave a variety of structures. In an embodiment, both the firstreflective layer 312 and the second reflective layer 314 are formed witha single layer, multiple layers, a divided layer structure, non-uniformstructures, or a combination thereof.

Because most materials absorb light at extreme ultraviolet wavelengths,the optical elements used are reflective instead of the transmissive asused in other lithography systems. The multilayer stack 306 forms areflective structure by having alternating thin layers of materials withdifferent optical properties to create a Bragg reflector or mirror.

In an embodiment, each of the alternating layers has dissimilar opticalconstants for the extreme ultraviolet light 112. The alternating layersprovide a resonant reflectivity when the period of the thickness of thealternating layers is one half the wavelength of the extreme ultravioletlight 112. In an embodiment, for the extreme ultraviolet light 112 at awavelength of 13 nm, the alternating layers are about 6.5 nm thick. Itis understood that the sizes and dimensions provided are within normalengineering tolerances for typical elements.

The multilayer stack 306 can be formed in a variety of ways. In anembodiment, the first reflective layer 312 and the second reflectivelayer 314 are formed with magnetron sputtering, ion sputtering systems,pulsed laser deposition, cathode arc deposition, or a combinationthereof.

In an illustrative embodiment, the multilayer stack 306 is formed usinga physical vapor deposition technique, such as magnetron sputtering. Inan embodiment, the first reflective layer 312 and the second reflectivelayer 314 of the multilayer stack 306 have the characteristics of beingformed by the magnetron sputtering technique including precisethickness, low roughness, and clean interfaces between the layers. In anembodiment, the first reflective layer 312 and the second reflectivelayer 314 of the multilayer stack 306 have the characteristics of beingformed by the physical vapor deposition including precise thickness, lowroughness, and clean interfaces between the layers.

The physical dimensions of the layers of the multilayer stack 306 formedusing the physical vapor deposition technique can be preciselycontrolled to increase reflectivity. In an embodiment, the firstreflective layer 312, such as a layer of silicon, has a thickness of 4.1nm. The second reflective layer 314, such as a layer of molybdenum, hasa thickness of 2.8 nm. The thickness of the layers dictates the peakreflectivity wavelength of the extreme ultraviolet reflective element.If the thickness of the layers is incorrect, the reflectivity at thedesired wavelength 13.5 nm can be reduced.

In an embodiment, the multilayer stack 306 has a reflectivity greaterthan 60%. In an embodiment, the multilayer stack 306 formed usingphysical vapor deposition has a reflectivity in a range of 66%-67%. Inone or more embodiments, forming the capping layer 308 over themultilayer stack 306 formed with harder materials improves reflectivity.In some embodiments, reflectivity greater than 70% is achieved using lowroughness layers, clean interfaces between layers, improved layermaterials, or a combination thereof.

In one or more embodiments, the capping layer 308 is a protective layerallowing the transmission of the extreme ultraviolet light 112. In anembodiment, the capping layer 308 is formed directly on the multilayerstack 306. In one or more embodiments, the capping layer 308 protectsthe multilayer stack 306 from contaminants and mechanical damage. In oneembodiment, the multilayer stack 306 is sensitive to contamination byoxygen, tantalum, hydrotantalums, or a combination thereof. The cappinglayer 308 according to an embodiment interacts with the contaminants toneutralize them.

In one or more embodiments, the capping layer 308 is an opticallyuniform structure that is transparent to the extreme ultraviolet light112. The extreme ultraviolet light 112 passes through the capping layer308 to reflect off of the multilayer stack 306. In one or moreembodiments, the capping layer 308 has a total reflectivity loss of 1%to 2%. In one or more embodiments, each of the different materials has adifferent reflectivity loss depending on thickness, but all of them willbe in a range of from 1% to 2%.

In one or more embodiments, the capping layer 308 has a smooth surface.For example, the surface of the capping layer 308 can have a roughnessof less than 0.2 nm RMS (root mean square measure). In another example,the surface of the capping layer 308 has a roughness of 0.08 nm RMS fora length in a range of from 1/100 nm to 1/1 μm. The RMS roughness willvary depending on the range it is measured over. For the specific rangeof from 100 nm to 1 micron, which roughness is 0.08 nm or less,roughness will increase over larger ranges.

The capping layer 308 can be formed in a variety of methods. In anembodiment, the capping layer 308 is formed on or directly on themultilayer stack 306 with magnetron sputtering, ion sputtering systems,ion beam deposition, electron beam evaporation, radio frequency (RF)sputtering, atomic layer deposition (ALD), pulsed laser deposition,cathode arc deposition, or a combination thereof. In one or moreembodiments, the capping layer 308 has the physical characteristics ofbeing formed by the magnetron sputtering technique including precisethickness, low roughness, and clean interfaces between the layers. In anembodiment, the capping layer 308 has the physical characteristics ofbeing formed by the physical vapor deposition including precisethickness, low roughness, and clean interfaces between the layers.

In one or more embodiments, the capping layer 308 is formed from avariety of materials having a hardness sufficient to resist erosionduring cleaning. In one embodiment, ruthenium is used as a capping layermaterial because it is a good etch stop and is relatively inert underthe operating conditions. However, it is understood that other materialscan be used to form the capping layer 308. In specific embodiments, thecapping layer 308 has a thickness in a range of from 2.5 to 5.0 nm.

In one or more embodiments, the absorber 310 is a layer that absorbs theextreme ultraviolet light 112. In an embodiment, the absorber 310 isused to form the pattern on the EUV reflective mask 106 by providingareas that do not reflect the extreme ultraviolet light 112. Theabsorber 310, according to one or more embodiments, comprises a materialhaving a high absorption coefficient for a particular frequency of theextreme ultraviolet light 112, such as about 13.5 nm. In an embodiment,the absorber 310 is formed directly on the capping layer 308, and theabsorber 310 is etched using a photolithography process to form thepattern of the EUV reflective mask 106.

According to one or more embodiments, the extreme ultraviolet reflectiveelement 302, such as the extreme ultraviolet mirror 205, is formed withthe substrate 304, the multilayer stack 306, and the capping layer 308.The extreme ultraviolet mirror 205 has an optically flat surface and canefficiently and uniformly reflect the extreme ultraviolet light 112.

According to one or more embodiments, the extreme ultraviolet reflectiveelement 302, such as the EUV mask blank 204 or phase shift mask, isformed with the substrate 304, the multilayer stack 306, the cappinglayer 308, and the absorber 310. The mask blank 204 has an opticallyflat surface and can efficiently and uniformly reflect the extremeultraviolet light 112. In an embodiment, the mask pattern 114 is formedwith the absorber 310 of the EUV mask blank 204.

According to one or more embodiments, forming the absorber 310 over thecapping layer 308 increases reliability of the EUV reflective mask 106.The capping layer 308 acts as an etch stop layer for the absorber 310.When the mask pattern 114 of FIG. 2 is etched into the absorber 310, thecapping layer 308 beneath the absorber 310 stops the etching action toprotect the multilayer stack 306. In one or more embodiments, theabsorber 310 is etch selective to the capping layer 308. In someembodiments, the capping layer 308 comprises ruthenium, and the absorber310 is etch selective to ruthenium.

Referring now to FIG. 5, an extreme ultraviolet reflective element 400,which in some embodiments is an EUV mask blank or an EUV phase shiftmask, is shown as comprising a substrate 414, a multilayer stack ofreflective layers 412 on the substrate 414, the multilayer stack ofreflective layers 412 including a plurality of reflective layer pairs.In one or more embodiments, the plurality of reflective layer pairs aremade from a material selected from a molybdenum (Mo) containing materialand silicon (Si) containing material. In some embodiments, the pluralityof reflective layer pairs comprises alternating layers of molybdenum andsilicon. The extreme ultraviolet mask reflective element 400 furtherincludes a capping layer 422 on the multilayer stack of reflectivelayers 412, and there is an absorber 420 on the capping layer 422. Inone embodiment, the absorber 420 comprises a first layer 420 a and asecond layer 420 b, which provides an absorber layer pair. In one ormore embodiment, the plurality of reflective layers 412 are selectedfrom a molybdenum (Mo) containing material and a silicon (Si) containingmaterial and the capping layer 422 comprises ruthenium.

In specific embodiments, there is plurality of absorber layer pairs,which provides a multilayer stack 420 of absorber layers including aplurality of absorber layer pairs 420 a, 420 b, 420 c, 420 d, 420 e, 420f, each pair comprised of (first layer 420 a/second layer 420 b, firstlayer 420 c/second layer 420 d, first layer 420 e, second layer 420 f).In one or more embodiments, the thickness of each of the first layer andthe second layer is optimized for different materials and applications,and typically in the range of 1-20 nm, such as from 1 nm to 9 nm, forexample, 4.5 nm. In one or more embodiments there are 3 to 40 bilayers,such as from 3 to 12, 3 to 11, 3 to 10, 3 to 9, 3 to 8, 3 to 7, 3 to 6,3 to 5, 4 to 13, 4 to 12, 4 to 11, 4 to 10, 4 to 9, 4 to 8, 4 to 7, 4 to6, 5 to 13, 5 to 12, 5 to 11, 5 to 10, 5 to 9, 5 to 8, 5 to 7, 6 to 13,6 to 12, 6 to 11, 6 to 10, 6 to 9, 6 to 8, 7 to 13, 7 to 12, 7 to 11, 7to 10, 7 to 9, 8 to 13, 8 to 12, 8 to 11, 8 to 10, 9 to 13, 9 to 12, 9to 11, 10 to 13, 10 to 12, or 11 to 13 bilayers.

In one or more embodiments, there is an absorber 420 on the cappinglayer, the absorber comprising bilayers comprising a first layer (e.g.420 a) of silicon and a second layer (e.g., 420 b). In one or moreembodiments, the second layer is a metal, and in specific embodiments, amaterial with an extinction coefficient (k value) higher than 0.035 andrefractive index (n value) lower than 0.95.

In one or more embodiments, the second layer is selected from the groupconsisting of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd,Co, Ag, Pt, oxides of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re,Os, Cd, Co, Ag, Pt, and nitrides of TaSb, CSb, TaNi, TaCu, Cr, Ir, Pd,Re, Os, Cd, Co, Ag, and Pt. In specific embodiments where each of thesecond layer materials is selected from the group TaSb, CSb, TaNi, TaCu,SbN, and CrN, the second layer is an alloy, and in more specificembodiments, each of these second layer materials is an amorphous alloy.

In one or more embodiments, the absorber 420 comprising the first layer420 a and the second layer 420 b forms a bi-layer structure. In one ormore embodiments, the mask blank comprises an etchable phase shift maskstack with “tunable” phase shift and reflectance values to optimize theperformance of absorber for different types of applications. Xxx In oneor more embodiments, the absorber 420 could achieve close to 215 degreesof phase shift with a reflectance between 6 and 15%. This could lead tosignificant improvement in the performance of the mask in terms of depthof focus (DOF), normalized image log slope (NILS) and telecentricityerror (TCE) comparing with the state-of-art Ta based absorbers.

DOF is associated with the process window size for a lithographyprocess. NILS is a measure of the quality of aerial image in alithography process. TCE is a measure of image shift with defocus in thelithography process. In one or more embodiments, mask blanks asdescribed herein provide the highest possible DOF and NILS with thelowest possible TCE.

In one or more embodiments, the first layer of the bilayer comprisessilicon. A range of materials when used together with the absorber ofthe bilayer, such as TaSb, could achieve close to 215 degrees of phaseshift with a reflectance between 6 and 15%. This could lead tosignificant improvement in the performance of the mask in terms of Depthof Focus (DOF), Normalized Image Log-Slope (NILS) and Telecentricityerror (TCE) comparing with the state-of-art Ta based absorbers. Othermaterials that can be used instead of TaSb include any material that isetchable with a high extinction coefficient (k value), such as CSb,TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, Pt, oxides ofTaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, Pt, andnitrides of TaSb, CSb, TaNi, TaCu, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, andPt.

In specific embodiments, the second layer comprises TaSb. In morespecific embodiments, the TaSb comprises a range of from about 21.9 wt.% to about 78.2 wt. % tantalum and a range of from about 21.8 wt. % toabout 78.1 wt. % antimony.

In specific embodiments, the second layer comprises CSb. In morespecific embodiments, the CSb comprises a range of from about 0.3 wt. %to about 3.6 wt. % carbon and a range of from about 96.4 wt. % to about99.7 wt. % antimony, or a range of from about 5.0 wt. % to about 10.8wt. % carbon and a range of from about 89.2 wt. % to about 95.0 wt. %antimony.

In specific embodiments, the second layer comprises SbN. In morespecific embodiments, the SbN comprises a range of from about 78.8 wt. %to about 99.8 wt. % antimony and a range of from about 0.2 wt. % toabout 21.2 wt. % nitrogen.

In specific embodiments, the second layer comprises TaNi. In morespecific embodiments, the TaNi comprises a range of from about 56.9 wt.% to about 94.6 wt. % tantalum and a range of from about 5.4 wt. % toabout 43.1 wt. % nickel.

In specific embodiments, the second layer comprises TaCu. In morespecific embodiments, the TaCu comprises a range of from about 74.0 wt.% to about 94.2 wt. % tantalum and a range of from about 5.8 wt. % toabout 26.0 wt. % copper, or a range of from about 13.0 wt. % to about65.0 wt. % tantalum and a range of from about 35.0 wt. % to 87.0 wt. %copper.

In specific embodiments, the second layer comprises SbN. In morespecific embodiments, the SbN comprises from about 78.8 wt. % to about99.8 wt. % antimony and from about 0.2 wt. % to about 21.2 wt. %nitrogen based upon the total weight of the compound.

In specific embodiments, the second layer comprises CrN.

In specific embodiments, the second layer comprises any one of Cr, Ir,Pd, Re, Os, Cd, Co, Ag, Pt, oxides of TaSb, CSb, TaNi, TaCu, SbN, CrN,Cr, Ir, Pd, Re, Os, Cd, Co, Ag, Pt, and nitrides of TaSb, CSb, TaNi,TaCu, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, and Pt.

According to one or more embodiments, the absorber layer pairs comprisea bilayer comprising a first layer (420 a, 420 c, 420 e) and a secondabsorber layer (420 b, 420 d, 420 f) each of the first absorber layers(420 a, 420 c, 420 e) and second absorber layer (420 b, 420 d, 420 f)have a thickness in a range of 0.1 nm and 10 nm, for example in a rangeof 1 nm and 5 nm, or in a range of 1 nm and 3 nm. In one or morespecific embodiments, the thickness of the first layer 420 a is 0.5 nm,0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm,1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, 2.1 nm, 2.2 nm, 2.3 nm,2.4 nm, 2.5 nm, 2.6 nm, 2.7 nm, 2.8 nm, 2.9 nm, 3 nm, 3.1 nm, 3.2 nm,3.3 nm, 3.4 nm, 3.5 nm, 3.6 nm, 3.7 nm, 3.8 nm, 3.9 nm, 4 nm, 4.1 nm,4.2 nm, 4.3 nm, 4.4 nm, 4.5 nm, 4.6 nm, 4.7 nm, 4.8 nm, 4.9 nm, and 5nm. In one or more embodiments, the thickness of the first absorberlayer and second absorber layer of each pair is the same or different.For example, the first absorber layer and second absorber layer have athickness such that there is a ratio of the first absorber layerthickness to second absorber layer thickness of 1:1, 1.5:1, 2:1, 2.5:1,3:1, 3.5:1, 4:1, 4.5:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1,14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or 20:1, which results in the firstabsorber layer having a thickness that is equal to or greater than thesecond absorber layer thickness in each pair. Alternatively, the firstabsorber layer and second absorber layer have a thickness such thatthere is a ratio of the second absorber layer thickness to firstabsorber layer thickness of 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1,5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1,18:1, 19:1, or 20:1 which results in the second absorber layer having athickness that is equal to or greater than the first absorber layerthickness in each pair.

According to one or more embodiments, the different absorber materialsand thicknesses of the absorber layers are selected so that thereflected extreme ultraviolet light is attenuated and with a change inphase due to interference of reflected light at bi-layer interfaces.While the embodiment shown in FIG. 5 shows three absorber layer pairs,420 a/420 b, 420 c/420 d and 420 e/420 f, the claims should not belimited to a particular number of absorber layer pairs. According to oneor more embodiments, the EUV reflective element 400 can include in arange of from 1 to 40 absorber layer pairs (2 to 80 total layers) or ina range of from 5 to 12 absorber layer pairs (10 to 24 total layers).

According to one or more embodiments, the absorber layers have athickness which provides 2-20% reflectivity and desirable etchproperties. A supply gas can be used to further modify the materialproperties of the absorber layers, for example, nitrogen (N₂) gas can beused to form nitrides of the materials provided above. The multilayerstack of absorber layers according to one or more embodiments is arepetitive pattern of individual thickness of different materials sothat the EUV light not only gets absorbed due to absorbance but by thephase change caused by multilayer absorber stack, which willdestructively interfere with light from multilayer stack of reflectivematerials beneath to provide better contrast.

Another aspect of the disclosure pertains to a method of manufacturingan extreme ultraviolet (EUV) mask blank comprising forming on asubstrate a multilayer stack of reflective layers on the substrate, themultilayer stack including a plurality of reflective layer pairs,forming a capping layer on the multilayer stack of reflective layers,and forming an absorber on the capping layer, the absorber comprising aplurality of bilayers comprising a first layer of silicon and a secondlayer selected from the group consisting of TaSb, CSb, TaNi, TaCu, SbN,CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, Pt, oxides of TaSb, CSb, TaNi,TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, Pt, and nitrides ofTaSb, CSb, TaNi, TaCu, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, and Pt.

In some embodiments, the first layer is formed by deposition of siliconby magnetron sputtering with Ar or Kr.

Exemplary embodiments of absorber configurations for an EUV reflectiveelement, for example an EUV mask blank or phase shift mask, are shown inTable 1.

TABLE 1 No. of Total Phase System Bilayers t (Si) t (Metal) ThicknessShift Reflectivity Cr—Si 9 2.2 nm 4.6 nm 61.2 nm 1.21 π 7.8% Cr—Si 9 3.2nm 3.7 nm 62.1 nm 1.19 π 9.6% TaSb—Si 7 3.6 nm 3.2 nm 47.6 nm 0.99 π5.2% TaSb—Si 9 2.6 nm 4.1 nm 60.3 nm  1.1 π 6.3% TaSb—Si 9   4 nm 2.9 nm62.1 nm  1.2 π 7.5%

The EUV mask blank can have any of the characteristics of theembodiments described above with respect to FIG. 4 and FIG. 5, and themethod can be performed in the system described with respect to FIG. 3.

In another specific method embodiment, the different absorber layers areformed in a physical deposition chamber having a first cathodecomprising a first absorber material and a second cathode comprising asecond absorber material. Referring now to FIG. 6 an upper portion of amulti-cathode chamber 500 is shown in accordance with an embodiment. Themulti-cathode chamber 500 includes a base structure 501 with acylindrical body portion 502 capped by a top adapter 504. The topadapter 504 has provisions for a number of cathode sources, such ascathode sources 506, 508, 510, 512, and 514, positioned around the topadapter 504.

In one or more embodiments, the alloys described herein comprise adopant. The dopant may be selected from one or more of nitrogen oroxygen. In an embodiment, the dopant comprises oxygen. In an alternativeembodiment, the dopant comprises nitrogen. In an embodiment, the dopantis present in the alloy in an amount in the range of from about 0.1 wt.% to about 5 wt. %, based on the weight of the alloy. In otherembodiments, the dopant is present in the alloy in an amount of about0.1 wt. %, 0.2 wt. %, 0.3 wt. %, 0.4 wt. %, 0.5 wt. %, 0.6 wt. %, 0.7wt. %. 0.8 wt. %, 0.9 wt. %, 1.0 wt. %, 1.1 wt. %, 1.2 wt. %, 1.3 wt. %,1.4 wt. %, 1.5 wt. %, 1.6 wt. %, 1.7 wt. %. 1.8 wt. %, 1.9 wt. %, 2.0wt. % 2.1 wt. %, 2.2 wt. %, 2.3 wt. %, 2.4 wt. %, 2.5 wt. %, 2.6 wt. %,2.7 wt. %. 2.8 wt. %, 2.9 wt. %, 3.0 wt. %, 3.1 wt. %, 3.2 wt. %, 3.3wt. %, 3.4 wt. %, 3.5 wt. %, 3.6 wt. %, 3.7 wt. %. 3.8 wt. %, 3.9 wt. %,4.0 wt. %, 4.1 wt. %, 4.2 wt. %, 4.3 wt. %, 4.4 wt. %, 4.5 wt. %, 4.6wt. %, 4.7 wt. %. 4.8 wt. %, 4.9 wt. %, or 5.0 wt. %.

In one or more embodiments in which the second layer of the absorber isan alloy, the alloy is a co-sputtered alloy absorber material formed ina physical deposition chamber. In one or more embodiments, the alloy ofthe second absorber layer can be co-sputtered by gases selected from oneor more of argon (Ar), oxygen (O₂), or nitrogen (N₂). In an embodiment,the alloy of the absorber layer can be co-sputtered by a mixture ofargon and oxygen gases (Ar+O₂). In some embodiments, co-sputtering by amixture of argon and oxygen forms and oxide of each metal of an alloy.In other embodiments, co-sputtering by a mixture of argon and oxygendoes not form an oxide of each metal of an alloy. In an embodiment, thealloy of the second absorber layer can be co-sputtered by a mixture ofargon and nitrogen gases (Ar+N₂). In some embodiments, co-sputtering bya mixture of argon and nitrogen forms a nitride of each metal of analloy. In other embodiments, co-sputtering by a mixture of argon andnitrogen does not form a nitride of a metal alloy. In an embodiment, thealloy of the absorber layer can be co-sputtered by a mixture of argonand oxygen and nitrogen gases (Ar+O₂+N₂). In some embodiments,co-sputtering by a mixture of argon and oxygen and nitrogen forms anoxide and/or nitride of each metal. In other embodiments, co-sputteringby a mixture of argon and oxygen and nitrogen does not form an oxide ora nitride of a metal. In an embodiment, the etch properties and/or otherproperties of the absorber layer can be tailored to specification bycontrolling the alloy percentage(s), as discussed above. In anembodiment, the alloy percentage(s) can be precisely controlled byoperating parameters such voltage, pressure, flow, etc., of the physicalvapor deposition chamber. In an embodiment, a process gas is used tofurther modify the material properties, for example, N₂ gas is used toform nitrides of the materials described herein.

In one or more embodiments, as used herein “co-sputtering” means thattwo targets, one target comprising a first metal and the second targetcomprising a second metal are sputtered at the same time using one ormore gas selected from argon (Ar), oxygen (O₂), or nitrogen (N₂) todeposit/form an absorber layer comprising an alloy of the materialsdescribed herein.

The multi-cathode source chamber 500 can be part of the system shown inFIG. 3. In an embodiment, an extreme ultraviolet (EUV) mask blankproduction system comprises a substrate handling vacuum chamber forcreating a vacuum, a substrate handling platform, in the vacuum, fortransporting a substrate loaded in the substrate handling vacuumchamber, and multiple sub-chambers, accessed by the substrate handlingplatform, for forming an EUV mask blank, including a multilayer stack ofreflective layers on the substrate, the multilayer stack including aplurality of reflective layer pairs, a capping layer on the multilayerstack of reflective layers, and an absorber on the capping layer, theabsorber layer made from the material described herein. The system canbe used to make the EUV mask blanks shown with respect to FIG. 4 or FIG.5 and have any of the properties described with respect to the EUV maskblanks described with respect to FIG. 4 or FIG. 5 above.

Processes may generally be stored in the memory as a software routinethat, when executed by the processor, causes the process chamber toperform processes of the present disclosure. The software routine mayalso be stored and/or executed by a second processor (not shown) that isremotely located from the hardware being controlled by the processor.Some or all of the method of the present disclosure may also beperformed in hardware. As such, the process may be implemented insoftware and executed using a computer system, in hardware as, e.g., anapplication specific integrated circuit or other type of hardwareimplementation, or as a combination of software and hardware. Thesoftware routine, when executed by the processor, transforms the generalpurpose computer into a specific purpose computer (controller) thatcontrols the chamber operation such that the processes are performed.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe disclosure. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the disclosure.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Although the disclosure herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present disclosure without departing from the spiritand scope of the disclosure. Thus, it is intended that the presentdisclosure include modifications and variations that are within thescope of the appended claims and their equivalents.

What is claimed is:
 1. An extreme ultraviolet (EUV) mask blankcomprising: a substrate; a multilayer stack which reflects EUVradiation, the multilayer stack comprising a plurality of reflectivelayer pairs; a capping layer on the multilayer stack which reflects UVradiation; and an absorber on the capping layer, the absorber comprisinga plurality of bilayers comprising a first layer of silicon and a secondlayer selected from a material with an extinction coefficient (k value)higher than 0.035 at a wavelength of 13.5 nm and refractive index (nvalue) lower than 0.95 at a wavelength of 13.5 nm, the material selectedfrom the group consisting of TaSb, CSb, TaNi, TaCu, SbN, Cr, Ir, Re, Os,Cd, Co, oxides of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Re, Os, Cd,and Co, and nitrides of TaSb, CSb, TaNi, TaCu, Cr, Ir, Re, Os, Cd, andCo, wherein the absorber provides a phase shift of 215 degrees and areflectance of 6-15% at 13.5 nm.
 2. The EUV mask blank of claim 1,wherein the second layer comprises TaSb.
 3. The EUV mask blank of claim2, wherein the TaSb comprises a range of from about 21.9 wt. % to about78.2 wt. % tantalum and a range of from about 21.8 wt. % to about 78.1wt. % antimony.
 4. The EUV mask blank of claim 1, wherein the secondlayer is selected from Cr, oxides of Cr and nitrides of Cr.
 5. The EUVmask blank of claim 4, wherein the absorber comprises from 3 to 40bilayers.
 6. The EUV mask blank of claim 1, wherein the second layercomprises TaNi.
 7. The EUV mask blank of claim 6, wherein the TaNicomprises a range of from about 56.9 wt. % to about 94.6 wt. % tantalumand a range of from about 5.4 wt. % to about 43.1 wt. % nickel.
 8. TheEUV mask blank of claim 1, wherein the second layer comprises CSb. 9.The EUV mask blank of claim 8, wherein the CSb comprises a range of fromabout 0.3 wt. % to about 3.6 wt. % carbon and a range of from about 96.4wt. % to about 99.7 wt. % antimony, or a range of from about 5.0 wt. %to about 10.8 wt. % carbon and a range of from about 89.2 wt. % to about95.0 wt. % antimony.
 10. The EUV mask blank of claim 1, wherein theabsorber comprises from 3 to 40 bilayers directly on the capping layerand the capping layer has a thickness in a range of from 2.5 nm to 5 nm.11. A method of manufacturing an extreme ultraviolet (EUV) mask blankcomprising: forming on a substrate a multilayer stack which reflects EUVradiation, the multilayer stack comprising a plurality of reflectivelayer pairs; forming a capping layer on the multilayer stack; andforming an absorber on the capping layer, the absorber comprising aplurality of bilayers comprising a first layer of silicon and a secondlayer selected from a material with an extinction coefficient (k value)higher than 0.035 at a wavelength of 13.5 nm and refractive index (nvalue) lower than 0.95 at a wavelength of 13.5 nm, the material selectedfrom the group consisting of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir,Re, Os, Cd, Co, oxides of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Re,Os, Cd, and Co, and nitrides of TaSb, CSb, TaNi, TaCu, Cr, Ir, Re, Os,Cd, and Co, wherein the absorber provides a phase shift of 215 degreesand a reflectance of 6-15% at 13.5 nm.
 12. The method of claim 11,wherein the second layer comprises TaSb.
 13. The method of claim 12,wherein the TaSb comprises a range of from about 21.9 wt. % to about78.2 wt. % tantalum and a range of from about 21.8 wt. % to about 78.1wt. % antimony.
 14. The method of claim 11, wherein the second layer isselected from Cr, oxides of Cr and nitrides of Cr.
 15. The method ofclaim 14, wherein the absorber comprises from 3 to 40 bilayers.
 16. Themethod of claim 11, wherein the second layer comprises TaNi.
 17. Themethod of claim 16, wherein the TaNi comprises a range of from about56.9 wt. % to about 94.6 wt. % tantalum and a range of from about 5.4wt. % to about 43.1 wt. % nickel.
 18. The method of claim 11, whereinthe second layer comprises CSb.
 19. The method of claim 18, wherein theCSb comprises a range of from about 0.3 wt. % to about 3.6 wt. % carbonand a range of from about 96.4 wt. % to about 99.7 wt. % antimony, or arange of from about 5.0 wt. % to about 10.8 wt. % carbon and a range offrom about 89.2 wt. % to about 95.0 wt. % antimony.
 20. The method ofclaim 11, wherein the absorber comprises from 3 to 40 bilayers directlyon the capping layer and the capping layer has a thickness in a range offrom 2.5 nm to 5 nm.